1. Field of the Invention
The present invention relates to footwear. The invention concerns, more particularly, a footwear outsole with a wear indicator.
2. Description of Background Art
An article of footwear generally includes an upper and a sole structure. The upper comfortably receives a foot and secures the foot to the sole structure. The sole structure provides a durable medium for supporting the foot and may include multiple elements, including a ground-contacting outsole.
The structure of an outsole may be selected from a variety of configurations that are specifically tailored to the intended purpose for which the footwear is designed. An outsole intended for running shoes, for example, may be formed from a durable synthetic material, such as rubber, that resists wear during use and may include a textured surface to enhance traction. An outsole for a dress shoe, however, may be formed from multiple layers of leather that incorporate rubber elements in high-wear areas. Similarly, an outsole for a skateboarding shoe may include portions that wrap onto the sides of the upper to provide wear resistance in areas that individuals drag along the ground for reducing the velocity of a skateboard. Accordingly, outsoles may have a variety of configurations, depending upon the intended purpose for the footwear.
An outsole forms the ground-contacting portion of an article of footwear and, therefore, may be subjected to high levels of wear. During running, for example, the rear-lateral corner of a running shoe initially contacts the ground and the running shoe then rotates forward such that a majority of the outsole is in contact with the ground. The heel portion of the outsole then disengages from the ground such that only the toe portion remains in contact. Finally, the runner propels forward utilizing only the toe portion of the outsole, a process termed toe-off, and the entire outsole is lifted from the ground to begin another cycle. At each phase of the running cycle where portions of the outsole are in contact with the ground, those portions experience abrasive forces from the ground. That is, portions of the outsole in contact with the ground experience wear that has the potential to eventually wear through the entire outsole in localized, high-wear areas. With regard to running, the high-wear areas may be the rear-lateral corner of the outsole, where initial contact with the ground occurs, and the toe portion of the outsole, where toe-off occurs.
Dress shoes and skateboarding footwear may also experience unique wear patterns that are dependent upon the manner in which the outsoles contact the ground. Like running shoes, dress shoes may experience high levels of wear in the heel and toe regions due to similarities in the running and walking cycles. Skateboarding shoes, however, generally experiences wear patterns that are distinct from the wear patterns associated with running and dress shoes. Although skateboarding shoes are utilized for walking and running, which may develop the wear patterns discussed above, the primary wear areas include portions of the skateboarding outsole that wrap onto the upper. During skateboarding activities, an individual may drag the skateboarding shoe against the ground in an effort to reduce the velocity of the skateboard. Generally, the toe portion of the skateboarding shoe, particularly the toe portions of the outsole that wrap onto the upper, are utilized for this purpose. Unlike running shoes and walking shoes, where the high-wear areas are concealed on the bottom portion of the footwear, high-wear areas of skateboarding shoes are prominently displayed and may be viewed as symbols of skateboarding prowess, particularly when the high-wear areas are worn in a manner that is severe or distinctive.
Although the degree of wear in outsoles may be viewed as a status symbol, as in skateboarding footwear, high levels of outsole wear may also detract from the utility of footwear. As the outsole wears away in running shoes, the midsole may become exposed. In general, midsole structures are formed from a foam material, such as ethylvinylacetate or polyurethane foam, that has a relatively small degree of wear resistance. High levels of outsole wear in running shoes may, therefore, develop areas in the shoes that permit stones or water to enter through the sole structure. Similar considerations are applicable to dress shoes and skateboarding shoes.
Individuals may usually determine whether an outsole is highly worn by inspecting the outsole visually. With running shoes and skateboarding shoes, the textured, traction-promoting surface may have a smooth aspect that signals high degrees of wear. Alternately, portions of the midsole or upper may be visible through the wear areas. With dress shoes, the leather portions of the sole may develop holes, or the thread that secures the sole structure to the upper may wear through such that the outsole separates from the upper. In general, these methods of determining wear only signal high degrees of wear that require replacement of the footwear or replacement of the sole structure.